1. Field of the Invention
The present invention relates to laser projection systems.
2. Description of the Related Art
The use of lasers in projection systems enables the creation of vibrant images with extensive color coverage that may be difficult to achieve by conventional (non-laser) light sources. One significant obstacle to laser image projection is the speckle phenomenon. Speckle arises when coherent light scattered from a rough surface, such as a screen, is detected by an intensity detector (e.g., a human eye) that has a finite aperture (e.g., a pupil). The finite aperture defines the spatial resolution of the detector and leads to quantization of the detected image into a mosaic of spots, the size of which is defined by the spatial resolution. For example, if light scattered from a spot on the screen interferes destructively at the detector's aperture, then that spot appears as a relatively dark spot in the detected image. On the other hand, if light scattered from a spot interferes constructively at the detector's aperture, then that spot appears as a relatively bright spot in the detected image. This apparent spot-to-spot intensity variation detected even when the screen is uniformly lit is referred to as speckle. Since speckle superimposes a granular structure on the perceived image, which both degrades the image sharpness and annoys the viewer, speckle reduction is highly desirable.